During the manufacture of semiconductor devices, various processes are conducted in a vacuum, such as etching, film forming, ashing process or sputtering. Separate vacuum processing units are used for these processes.
One type of conventional vacuum processing unit is the "cluster-tool" processing unit. It comprises a plural vacuum processing chamber, a conveying chamber connected to the plural vacuum processing chamber, an auxiliary vacuum chamber connected to the conveying chamber and having a load-lock mechanism, and a passing chamber connected to the auxiliary chamber. A conveying arm is typically provided in the conveying chamber for conveying substrates to be processed.
In the above vacuum processing unit, the conveying chamber and the plural vacuum chambers are maintained at a certain vacuum. Substrates such as wafers are passed from a transfer chamber to the conveying chamber through the auxiliary vacuum chamber. They are then conveyed by the conveying arm into their designated vacuum processing chambers where they undergo various processes. After being processed, they are conveyed back into the auxiliary vacuum chamber by the conveying arm and are passed back into the transfer chamber.
The auxiliary vacuum chamber is disposed between the transfer chamber which is kept at atmospheric pressure and the conveying chamber which is kept at a vacuum. The auxiliary vacuum chamber is maintained at a vacuum when semiconductor wafers are conveyed into and out of the conveying chamber, and is returned to atmospheric pressure when semiconductor wafers are conveyed into and out of the transfer chamber.
The auxiliary vacuum chamber has means for heating or cooling semiconductor wafers in preparation for the succeeding processing step. In addition, the auxiliary vacuum chamber may conduct degassing on the semiconductor wafers by means of heating.
The above auxiliary vacuum chamber has gates between the auxiliary vacuum chamber and other chambers to enable repeating the switching between atmospheric pressure and a vacuum. This makes costs high. In addition, repeated switching between the atmospheric pressure and the vacuum takes much time as gas has to be supplied into/removed from the entire auxiliary vacuum chamber. This prevents improvement of the throughput for all of the processes.
There have been proposals for making the interior of the whole auxiliary vacuum chamber in a vacuum to avoid the necessity to switch between atmospheric pressure and a vacuum. However, such a unit would also need a hermetically closed space for heating or cooling semiconductor wafers, and so would need gates between the auxiliary vacuum chamber and the other chambers.